Glad you got it done "properly." My experience is that overlay installs for me have worked just fine. I did a "clean" install of Mavericks, but that was because I had decided to install an internal SSD from which to boot, so a clean install was required. I know most folks recommend "clean" installs, and that is a good recommendation to avoid any potential problems that could come up if the update install goes south. But as I said, they have worked for me just fine.